1. Field of the Invention
The present invention concerns pneumatic pressure pads, or actuators, for cyclically applying pressure forces evenly over an area. The present invention particularly concerns cyclically evenly pressuring an exposed master microfiche film into contact with an unexposed sensitized photographic film at an exposure station of a microfiche duplicator equipment by cyclical application of pressure forces from a reciprocating pneumatic pressure pad.
2. Background of the Invention
Machines for the duplication of film, and particularly microfilm and microfiche, are known. Some such machines are manufactured by Anacomp, Inc.--assignee of the present invention--at its Data Systems Division, and are supported by its Micrographics Engineering Division, P.O. Box 82449 San Diego, Calif. 92138. The duplication machines are commonly used to make multitudinous copies of a single microfilm, or microfiche, master that has typically been generated by, and during, a Computer Output on Microfilm (COM) process. Distribution of the duplicated microfilm or microfiche is an efficient way of disseminating voluminous amounts of information such as, for example, banking transaction records.
The images that appear upon the master, and upon the duplicated, films are typically word and number images. These images are commonly of type fonts, typically as small as 6 points in size, which have been optically reduced at magnification ratios commonly ranging to 96.times.. These minutely-sized images, and certain still smaller features that result from reducing original images smaller than 6 point type and/or at magnification ratios higher than 96.times., demand that the duplication process should be very exacting, and of high quality. Meanwhile, a duplication rate on the order of 2000 copies per hour per duplication machine is typically required if certain large data bases maintained on microfilm or microfiche, such as the data bases generated by large multi-branch banks, are to be replicated each business day by the use of reasonable numbers--on the order of tens--of duplication machines.
The existing duplication machines that perform quality duplication at the required rates typically use the vesicular process: a copy film that has been exposed from a master film is developed by heat alone, and without use of any chemicals or gases. The duplication process is image reversing in that a negative master will produce a positive copy.
One station within a microfilm or microfiche duplication machine is an exposure station. At this station successive unexposed copy films, or successive regions of a roll of unexposed copy film, are exposed, one copy film or copy film region at a time, from a master film. The master film is typically held in a fixture, or jig. It and the copy film must be pressed together into tight uniform contact, and then exposed to a light (or other exposing radiation) source. In order that the fine detail of the image upon the master film should expose without appreciable distortion or blurring onto the copy film, it is necessary that the copy and master films, which are each flexible, should be held together with great uniformity, and without inducing bowing or wrinkling in either film.
This required pressing of a copy film and a master film into close uniform contact at the exposure station of a film, and particularly a microfiche, duplication machine has proven to be troublesome--especially when this pressing has been attempted to be cyclically repetitively accomplished at required high rates, typically faster than one cycle every two seconds. One existing mechanism for realizing the necessary close contact of the master and copy films during an exposure of the copy from the master is based on a moving mechanical stage called an "expose activate assembly". The expose activate assembly consists of (i) a solenoid-operated hook that holds a carriage bearing the copy film to be exposed in an exposure area, which hook is mounted to (ii) a motor-driven eccentric shaft that raises and lowers a platen to force the copy film upon the carriage into pressured contact with a master film that is simultaneously held upon a jig, or fixture. After exposure of the copy film the platen retracts, relieving the contact pressure, and the solenoid is energized so as to raise the hook, and permit the carriage to return to the load position.
The particular part of this particular previous mechanism that is of most relevance to the present invention is its moving platen. It is the planar surface of this platen that is used to press the copy film (as held upon the carriage) and the master film (as held in a jig) into tight contact. Alas, the alignment of the platen, and the results of its movement, are troublesome.
First, the platen must be both horizontally and vertically adjusted, or registered, relative to the master microfiche which is being copied. The horizontal and vertical adjustments determine that the copy film, as held upon the carriage which is moved by the platen, is, as such copy film is brought into pressured contact with the master fiche, of proper position relative to the image that is within the plane of such master microfiche. In order that film should not be wasted, the required registration of the image area of the copy film to the imaged area of the master fiche is typically quite exacting, and on the order of 0.010 inches (0.25 mm). A horizontal adjustment, or registration, of this precision is realized by four detents, each providing a 0.010 inch (0.25 mm) shift in platen position. A vertical adjustment, or registration, of this precision is obtained by two screws that position and align the platen relative to the carriage. Each turn of the vertical adjusting screws normally produces 0.03 inch (0.81 mm) of relative movement.
These adjustments, although sensitive, are not unsatisfactorily troublesome in and of themselves. Unfortunately, in the previous "expose activate assembly" mechanism at least the vertical adjustment within the image plane exhibits an undesirable interplay with a remaining, "z"-axis, adjustment. The "z"-axis, or up-down, adjustment determines that the plane of the copy film as held upon the carriage which is moved by the platen is, as such copy film is brought into pressured contact with the master fiche (held stationary upon a jig), everywhere parallel to the plane of such master fiche. In the previous "expose activate assembly" this adjustment is realized by four adjusting screws, and accompanying lock nuts, that are located at the four corners of the platen. The screws must be adjusted, and locked, so as to both (i) establish proper clearance between the platen and the carriage (holding the copy film), and (ii) establish the plane of the platen to be parallel to the plane of the copy film as held upon the carriage (and also to the plane of the master fiche as held upon the jig). The adjustment of both (i) play and (ii) parallelism is desirably to an accuracy of 0.005 inch (0.10 mm).
All these adjustments are, of course, desirably made and maintained at the indicated tolerances in order to ensure a repetitively reliable and quality duplication of microfiche. They are difficult to so make, and to maintain. In particular, the carriage and the copy film held upon the carriage are reciprocated relative to the frame, and relative to the master film that is fixedly held relative to the frame, not along an axis that is orthogonal to the plane of such master film, but rather along an axis that is skewed relative to this plane. This occurs because the platen is mounted to the duplication machine frame by a "bicycle-chain-type" linkage, and is constrained by this linkage in its movement. The resultant movement of the platen in direction which is not orthogonal to the plane of the mater film causes the previously mentioned interplay between the vertical adjustment(s) and the up-down adjustment(s).
This interplay, as well as the intricacy of the numerous adjustments themselves, make maintenance of the expose activate assembly undesirably labor intensive. Moreover, even such maintenance as is painstakingly and exactingly performed is--innately because of the non-orthogonal movement of the platen and of the copy film borne thereon relative to the master film during their movement together into pressured contact--of uncertain reliability to realize the uniform pressured contact between the two films that is mandated for high-quality duplication.
Another duplication equipment of Anacomp Inc., assignee of the present invention, also pressures a master and a copy film into tight contact at an exposure station while exhibiting fewer problems in so doing. This other equipment relies on a pneumatic bladder, or membrane. The elastomeric bladder is stretched across a rectangular chamber. The films that are to be pressured together are located on one side of the chamber and its bladder. Application of pneumatic pressure within the chamber, and on the opposite side of the bladder to the films, causes the bladder to expand towards the films, pressing the films into contact.
Although this mechanism, and method, is generally more precise and reliable than a mechanism based on moving stages connected by linkages, it also has limitations. The pneumatic bladder is subject to failure, especially where it abrades and stretches against the right-angle corners of the rectangular chamber. Because, upon release of the expansion air pressure, a return of the expanded bladder to its undistended position is based on the bladder's elastomeric properties, cycle speeds are limited. The evenness at which the pressure force may be applied over the area(s) of the workpiece film(s) is limited. Precision in control of the direction at which the pressure force is applied over the area(s) of the workpiece film(s) is limited.
As regards the (i) evenness, and (ii) direction, at which a pressure force is best applied over a prescribed area, it has been found that photographic films are most satisfactorily pressured into uniform, defect-free, even contact if the moving member that contacts such films is not precisely planar, but is very slightly (on the order of a few thousandths of an inch) crowned, or domed. Such a substantially planar crowned member is desirably moved in a direction precisely orthogonal to the plane(s) of the film(s). So moved and contoured, it serves to first, and (very slightly) most tightly, pressure the films together at the center of their image areas. Then the applied pressure force is successively radiated to ever more peripheral regions about this center as the crowned member is brought into ever closer proximity, and into ever stronger pressured contact, with the films.
In summary, it would be desirable to be able to cyclically pressure two flexible planar, film, workpieces into momentary tight physical contact with a high degree of reliability, repeatability, and precision. The film workpieces must be forced, or pressured, together in a manner that preserves the registration of an image area that is to be exposed upon a copy film with a corresponding exposed image area upon a master film. Equally importantly, each of the film workpieces must be forced to lie precisely in a plane without wrinkles, bows, bulges, mounds, creases, or anything else that extends above or below the plane--even minutely and/or over but a small localized region. Finally, the planes of the two film workpieces should be very precisely parallel to each other, and should lie proximate to each other insofar as the physical thickness of the films permit.